The Belgian outfit host their Czech foes at the Constant Vanden Stock Stadium after falling to a 3-1 defeat last week, although a late own goal has given the hosts a slice of hope.
Match preview
In what was the recently-appointed Pocognoli's first European match in charge of Union SG, the 37-year-old cut a downcast figure on the touchline as Slavia Prague stormed into a three-goal advantage inside 57 minutes of last week's opening encounter.
Slavia's aerial mastery - and more specifically that of Tomas Chory - came to the fore in the first half, as the 29-year-old notched a pair of headers before Oscar added some gloss to the scoreline, although Alexandr Buzek's 73rd-minute own goal was a blot on the Slavia notebook.
Any hopes of Union SG reducing the deficit further were extinguished when substitute striker Mohammed Fuseini was sent off for violent conduct in the dying embers, but a two-goal disadvantage is not unassailable for the Belgian upstarts, who are yet to reach the Champions League proper.
Pocognoli and co can kiss such hopes goodbye if their recent streak of defensive failures is anything to go by; after last week's 3-1 first-leg loss, Union SG went down 4-3 to Westerlo in Jupiler Pro League action, where a late fightback from 4-1 down proved futile.
Now at risk of suffering three straight losses for the first time since a run of four in April, Les Unionistes will be forced to accept a place in the Europa League league phase should they fail to pull off a terrific turnaround on Tuesday, where the form book certainly favours their Czech counterparts.
Already engaging in another heated scrap for Czech footballing supremacy with bitter rivals Sparta Prague - who pipped them to the title by just four points last season - Slavia Prague are once again playing catch-up in their quest for 2024-25 glory.
An opening-day goalless draw with Slovacko preceded three straight wins over Ceske Budejovice, Slovan Liberec and Sigma Olomouc for Jindrich Trpisovsky's men, who eased to a 2-0 victory over the former on Saturday, but Sparta's perfect haul of 12 points from 12 means that Slavia are settling for second right now.
However, domestic matters now take a back seat while Slavia continue in their quest for just a third appearance in the Champions League group stage, having qualified for the 2007-08 and 2019-20 editions but failing to progress further on both occasions.
Victims of a 7-3 aggregate loss to AC Milan in last year's Europa League last 16, Slavia Prague have since reverted to type and arrive in Belgium with a 12-match unbeaten run across all competitions to protect, as well as a four-game winning sequence in which they have shipped just one goal.
Either Ligue 1 side Lille or Turkish titans Fenerbahce will be waiting to take on Slavia Prague in the playoff round should Trpisovsky's men avoid a Belgian beatdown on Tuesday, but the losers will not have to endure the rigmarole of another preliminary match to reach the Europa League proper, unlike teams in the Champions path.
Union SG Champions League form:
L
Union SG form (all competitions):
Slavia Prague Champions League form:
W
Slavia Prague form (all competitions):
Team News
Owing to his red card for violent conduct in the dying embers of last week's first leg, Union SG striker Fuseini will sit on the naughty step for Tuesday's return fixture, although a start was likely out of the question regardless.
Fuseini actually completed the full 90 minutes in the weekend's league defeat, but Dennis Eckert Ayensa, Promise David and Elton Kabangu will now compete to partner Kevin Rodriguez, who struck an inconsequential brace on Saturday.
Manager Pocognoli was also sent off right at the death in the Westerlo loss, but his suspension only applies to domestic matches. However, two English defenders - Ross Sykes and Christian Burgess - are both out with foot problems, while Lazare Amani is nursing a knock too.
In contrast, Slavia Prague have a clean bill of health disciplinary wise, but a quartet of rearguard enforcers are absent through injury, including goalkeeper Jindrich Stanek and left-back Ondrej Zmrzly.
Central defenders Tomas Vlcek and Stepan Chaloupek are also out of contention; the former could be out until the last few weeks of the season due to a knee operation, but Trpisovsky has no need to make major alterations either way.
The Slavia boss could afford to rotate for the weekend's victory over Sigma Olomouc, meaning that key men such as Chory, Lukas Provod and Euro 2024 hero Ivan Schranz will return to the first XI with fresh legs.
Union SG possible starting lineup:
Moris; Castro-Montes, Mac Allister, Machida, Leysen; Rasmussen, Sadiki, Vanhouette; Puertas; Eckert Ayensa, Rodriguez
Slavia Prague possible starting lineup:
Kinsky; Prebsl, Ogbu, Zima; Masopust, Oscar, Zafeiris, Diouf; Schranz, Chory, Provod
We say: Union SG 1-2 Slavia Prague (Slavia Prague win 5-2 on aggregate)
As Slavia Prague pack more of an attacking punch and can be sure to capitalise on Union SG's defensive shortcomings, the Czech outfit ought to successfully fight fire with fire in Belgium.